The present invention relates to a tilt amount detector for processing a signal which is read from an optical disc using an optical pickup and a tilt corrector for correcting tilt in accordance with a tilt amount detected by the tilt amount detector. The present invention also relates to an optical disc apparatus for implementing the tilt amount detector and the tilt corrector.
With development of an information-oriented society, there has been an increasing number of occasions where users desire to freely record/reproduce data in multiple formats using a single medium. Such data includes music data, video data, and computer application data, for example. Particularly, for disc type recording media such as CDs (Compact Discs), MDS (Mini Discs), and DVDs (Digital Versatile Discs) (each hereinafter referred to as an optical disc), further increase in capacity is demanded. Newly introduced disc formats that permit high-density recording of information have become of major interest as next-generation recording solutions.
In a recording/reproducing apparatus which uses such an optical disc mentioned above as a recording medium, a radial tilt angle and a tangential tilt angle are controlled which represent the tilt of the optical disc in a radial direction and a tangential direction, respectively, with respect to an optical spot irradiated from an optical pickup. Along with the increase in recording density, ensuring high reliability of recording/reproducing performances has become a major concern. To achieve such reliability, it is crucial to detect an amount of tilt displacement of the optical disc with high precision and control the detected tilt.
According to a known recording/reproducing apparatus, an optical pickup is moved in a positive or a negative direction so that an amount of tilt displacement can be obtained from an angle between the optical disc and the optical pickup, and an optimum tilt position is determined using the obtained tilt amount. Thus, this configuration can be implemented in conjunction with a physical arrangement which serves to move the optical pickup to detect a tilt angle of the optical pickup for achieving a smallest jitter value. Consequently, it may be impossible for an apparatus without such a physical arrangement to obtain a tilt amount after being installed with an optical pickup.
A configuration of a known optical disc apparatus is illustrated in FIG. 7. An optical disc apparatus 100 includes an optical pickup section 101, an RF amplifier section 102, and a DSP section 103, and a driver amplifier section 104, which are integrally controlled by a microcomputer 105.
As shown in FIG. 7, the optical pickup section 101 has a laser diode (LD) 111 for irradiating predetermined recording/reproducing laser light onto an optical disc 90, a grating 112 for dividing the light beam into a plurality of light beams, a beam splitter 113 for changing the direction of a propagation path for a light beam incident from the LD 11 and also transmitting a light beam reflected from the optical disc 90, a collimator lens 114 for collimating a light beam, an objective lens 115 for converging a light beam onto a recording surface of the optical disc 90, a multi-lens 116 for converging the light beam reflected from the optical disc 90 onto a photodetector, and a photodetector 117 for converting the light beam reflected from the optical disc 90 into an electrical signal. The optical pickup section 101 includes a tilt sensor 118 for detecting a tilt angle of the optical pickup section 101.
Laser light emitted from the LD 111 is divided by the grading 112 into a plurality of light beams. Each of the light beams then passes through the beam splitter 113 and the collimator lens 114 and is converged by the objective lens 115 onto an information recording surface of the optical disc 90. The light beam reflected from the optical disc surface then travels through an optical system providing a return path in the optical pickup section 101 and enters the photodetector 17. The returning reflected beam is converted into an electrical signal by the photodetector 117. The electric signal is then transmitted to the RF amplifier section 102.
The RF amplifier section 102 includes an RF amplifier 121 for amplifying an RF signal, a servo amplifier 122, and an amplifier 123 for amplifying a signal detected by the tilt sensor 118. The DSP section 103 includes an RF equalizer 131 for correcting or adjusting the frequency characteristic or the like of an RD signal, a decoder 132 for decoding a separated component, a servo control circuit 133 for generating a servo control signal, and a tilt control circuit 134 for generating a control signal for controlling driving of a tilt motor (not shown) in accordance with the signal detected by the tilt sensor 118.
A signal output from the photodetector 117 is transmitted to the RF amplifier 121 and the servo amplifier 122 for RF signal calculation and servo signal calculation, respectively. Then, the output from the RF amplifier 121 is transmitted to the DSP section 103 for decoding a signal recoded on the optical disc 90. The output from the servo amplifier 122 is transmitted to the driver amplifier section 104. The servo signal is amplified by the amplifiers 141 and 142 and then transmitted to a biaxial actuator and an LD (not shown). The signal output by the tilt sensor 118 is amplified by the amplifier 123 and transmitted to the tilt control circuit 134. The tilt control circuit 134 generates a tilt motor control signal for controlling driving of a tilt motor (not shown). The tilt motor control signal is amplified by the amplifier 143 and transmitted to the tilt motor.
The foregoing operation is controlled by the microcomputer 105 which performs tasks associated with each circuit included in the DSP section 103 and the driver amplifier section 104, using serial/parallel signal processing. The tasks of the microcomputer 105 include providing instructions of On/Off switching, coefficient calculations, value setting, etc.
The optical pickup section 101 in FIG. 7 is generally referred to as an optical pickup (hereinafter referred to as an OP). The OP constitutes a mechanical deck for an optical disc drive in conjunction with other components such as a spindle motor, a sled motor, and a chassis which acts as driving means for rotating the optical disc 90.
In installing the OP in to the mechanical deck, in general, extremely high precision is expected with respect to the installation position and angle, particularly, in terms of a tilt direction, which is herein described as a major concern. Tilt can cause degradation of signal reproduction performance in accordance with the amount of the tilt. Tilt adjustment can be performed in accordance with a jitter value, which is widely used as an evaluation value of an RF signal.